The Choomahs are the main antagonists of the show. The Choomahs are a fictional species of wildly ferocious creatures who originated on Choomah Island as a mutation from Clarence's failed experiment. Choomahs often appear in the show in the backgrounds of scenes unbeknownst to other characters but will also sometimes attack characters. Each series of the show culminates in some form of assault on the Choomahs, in an attempt to rid Brown Town and their island of the species. Choomahs are very violent in nature and attack people when provoked.

Choomahs apparently reproduce and evolve extremely quickly, as they have learned to speak English and express remorse for their prior violence at the end of Choomah Island 3, whereupon they fly off to an unknown destination, the leader opining: "You know what? I'm really gonna miss this planet". The extent of their prior association with King Laranox remains unclear, but the recurring Bumble Brutus appeared to answer directly to Laranox.